2254C build/support thread

got the irons today. and fired up the first channel. compression is working.. but ;-) it sounds like passed through a lo-pass filter... what could be the problem ? i connectet the irons via the molex connectors. is the writing on the pcb correct? anybody got a voltage chart?

Check input/output Molex connectors on PCB 1+ 2gnd 3-
Check transformer's wiring
When going balanced to unbalanced short -output of in(out) to gnd
Etc

hmm connections seems to be right.
today i finished the second channel soldered the irons direct on the pcb and same problem occurred here. compression, sidechainfilter aso. is working i think but ther is something like a lo-pass filter on the whole signal. Is it right to use for TR1 9046 and for TR2 9045. maybe i used wrong caps for c´´11 680p; c2´´ 220nF; c5´´ 330nF ? EDIT: are these the right values??
I also connected no meters untill now but this should be no problem right?

thanks for your help!

maybe i used wrong caps for c´´11 680p; c2´´ 220nF; c5´´ 330nF ? EDIT: are these the right values??

Click to expand...

Right values are 680PF, 220PF, 330PF
220=220pF etc

F
Amen
/well, kidding, used same as shown at schematic with TF10015/16

Just finished up my 2254's (finally!)  And just in time for some mixing on the new Posies record.  Didn't even calibrate them yet (other than biasing) - they sound great!  I especially like the sound of the makeup gain/output section driving the transformers.  so much so that I built some 10dB pads so I wouldn't clip the converters on the way back in.  Once I get a free day I'll do the meter scale and calibrate the whole deal, but for now I'm having too much fun mixing.  I used Tat's case, and it looks pretty good.  Thanks Igor and group!


sorry about the crappy iPhone camera

HURRAY!!!!!!

next good news: i changed the two caps with wrong value to the right value 220p and 330p and the unit now sounds great. i will install a switch on the back with a few different attack/release timing caps.

So I finally got a few days free to calibrate this thing.  Bias is good, 3V cv is good, but I can't get the gain down to unity.  I'm at the bottom of the trim pot and I'm still almost 5 dB above unity, making the other calibrations a little tricky. Should I just change R"19 (in series with the trim pot) from 820 Ohms down to something smaller?  Or is there possibly something wrong elsewhere causing the gain to be weird?

so.. where are people getting their BC214s? ebay?

or has anyone tried substituting something from the current production BC5XX series?

BC212 will work as well as BC177/179.
No need for high beta, 140...500 is quite enough.
Check transistor's pinout /(datasheet!!!) to avoid headache with getting the thing working

thanks igor! i think i might have some BC179s in my parts collection. i'll check the pinout for sure.

i'm getting closer to finishing my stereo 2254C, about half way stuffed - i have a big package on the way from mouser, including most of the remaining parts. fedex says it'll arrive on my birthday - happy coincidence! 

so i also have some problems with the calibration.. i could not get the gain down so i lowered the 820 resistor to 715 but its not nearly enough. if i trimm the rv2 controllvoltage its no problem to get the gain down but then the next step is the problem.. with 3v on the link i can only get down to 0.402 what im doing wrong.. i rechecked and tryed a lot the last days ;-)

@Haima: all the best! How old you become?
@king-rb: can you please explain the problem in other words to let me a try to help?
What is your comp's gain without compression? (I.e. can you get to unity gain without
compression/makeup?)
Which 820R you mean and at which calibration stage you can't get down
the gain?

igor - i turn 31 years young tomorrow 8)

i'm planning a nice day in the workshop stuffing my 2254 boards! thanks for all the great projects and support you give us. big thumbs up!

okay sorry ;-) other words:
>i changed the R``19 to 715R
>input gain is 0.775V AC
>with the gain trim i can get to 1.150V AC minimum
>i have to trim RV2 Controller Voltage to get the gain down to 0.775V AC
>but then i dont have enough space to get the voltage down to 0.308 with the 3v on the Link
aso...
i used bc177 instead of bc214

Editing my question as I have figured some things out. I have read this whole thread, and I am sorry if I missed what I am about to ask. For a mono unit, I need a 15VA 2 x 12V toroid. 30 VA is only needed for a dual version. So far so good?

Re: availability of BC214 - i found futurlec has them for a pretty good price:

http://www.futurlec.com.au/price1.jsp?part_no=BC214

i just ordered a batch. remains to be seen what brand etc they are... i'll post my results here 

Great! Ordered a few of this.. so maybe then i will have not such big problems with the calibration...

king-rb: theoretically, i believe the BC177 should work fine - so don't rule out another source for your calibration issue...

but there's a possibility swapping them for BC214 might save you - hope so!